There exist a great number of conventional technologies for image sensors that have a wide dynamic range that permits favorable imaging even in cases where a very bright portion and a dark portion exist simultaneously. A large number of systems exist as processes that widen the dynamic range toward high illuminance on a CMOS image sensor.
Proposed systems include (1) a system that calculates the number of clocks until a photodiode reaches a threshold value that is set from the outside by disposing a comparator and a coefficient unit in a pixel circuit, as disclosed in Japanese Patent Application Laid Open No. H7-274072, (2) a system that calculates the number of times a photodiode reaches a threshold value that is set from the outside in one frame cycle by disposing a comparator and a coefficient unit in a pixel circuit, as disclosed in Japanese Patent Application Laid Open No. 2000-253320, (3) a system that accumulates blooming charge of the photodiode in floating diffusion in a period that is sufficiently shorter than one vertical period in a four-transistor pixel circuit and (4) a system that finds the difference between the signal level and the reset level from the signal part that accumulates in a period that is sufficiently shorter than one vertical period by means of a signal detection portion, as disclosed in Japanese Patent Application Laid open No. 2001-169184 and Japanese Patent Application Laid Open No. 2001-186414 respectively, (5) a system that uses floating diffusion of a four-transistor pixel circuit as described in “A High Dynamic Range CMOS APS Image Sensor” published in “the 2001 IEEE Workshop on Charge-Coupled Devices and Advanced Image Sensors”, pp 137-140 by Yibing (Michelle) Wang and others as an O/E conversion element of low sensitivity for high illuminance, (6) a system that finds a pixel value by means of floating point notation from the accumulation time and the read signal level that appear in U.S. Patent Publication Nos. 6175383 and 6369737, and 2002/0027606 and “100000-Pixel, 120-dB Imager in TFA Technology” of the IEEE Journal of Solid State Circuits, Vol. 35, No. 5, (7) a system that uses a logarithmic compression pixel circuit in which the signal voltage is logarithmically changed with respect to the incident light amount, as disclosed in Japanese Patent Application Laid Open No. 2000-83198 and Japanese Patent Application Laid Open No. 2002-77733, and (8) a system (U.S. Pat. No. 6,115,065) that seeks to widen the dynamic range by acquiring a long-time accumulation signal and short-time accumulation signal by also reading a row of signals displaced by Δ when performing signal reading of the nth row in the CMOS image sensor and by mixing the long-time accumulation signal and short-time accumulation signal, and so forth.